Metal chalcogenide film and method and device for manufacturing the same

ABSTRACT

Provided are a metal chalcogenide thin film and a method and device for manufacturing the same. The metal chalcogenide thin film includes a transition metal element and a chalcogen element, and at least one of the transition metal element and the chalcogen element having a composition gradient along the surface of the metal chalcogenide thin film, the composition gradient being an in-plane composition gradient. The metal chalcogenide thin film may be prepared by using a manufacturing method including providing a transition metal precursor and a chalcogen precursor on a substrate by using a confined reaction space in such a manner that at least one of the transition metal precursor and the chalcogen precursor forms a concentration gradient according to a position on the surface of the substrate; and heat-treating the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2018-0051818, filed on May 2,2018 in the Korean Intellectual Property Office, the disclosure of whichis incorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to metal chalcogenide thin films andmethods and devices for manufacturing the same, and more particularly,to metal chalcogenide thin films having an in-plane composition gradientalong a two-dimensional thin film, and methods and devices formanufacturing the same.

2. Description of Related Art

Elements belonging to Group 16 of the Periodic Table, for example,oxygen (O), sulfur (S), selenium (Se), tellurium (Te) and polonium (Po),may be referred to as oxygen group elements, from which the threeelements of sulfur, selenium, and tellurium may also be elements of thesulfur group, or chalcogens.

Oxygen and sulfur are representative non-metallic elements, but as theatomic number increases, the other elements lose their non-metallicityand have enhanced metallicity. Selenium, tellurium, and polonium arerare elements, and polonium is a natural radioactive element.

Metal chalcogenides are compounds including a transition metal and achalcogen, and may be a nanomaterial having a structure that is similarto graphene. The thickness of metal chalcogenides may be an atom-numberthickness and may be very small. Thus, metal chalcogenides may beflexible and transparent, and in an electric aspect, shows similarproperties of semiconductors, conductors, or the like.

Especially, in the case of semiconducting metal chalcogenide, due to anappropriate bandgap and electron mobility of several hundreds cm²/V·s,semiconducting metal chalcogenides may be suitable for applications insemiconductor devices, for example as transistors, and have greatpotential for future flexible transistor devices.

MoS₂ and WS₂, which are among the most actively studied materials amongmetal chalcogenide materials, have a direct bandgap in a single-layerstate, and thus, the absorption of light may efficiently occur, andthus, these materials may be suitable for the application to opticaldevices such as optical sensors and solar cells.

Methods of manufacturing such metal chalcogenide nano thin films havebeen actively studied recently. In order to apply such a metalchalcogenide thin film to the devices described above, for example,methods capable of synthesizing a thin film uniformly and continuouslyover a large area would be desired.

However, metal chalcogenide thin films with compositional variations maybe beneficial. Due to the metal chalcogenide thin film having acompositional variation, the electric and optical bandgap may vary, anda region that is turned on (depending on the input energy band of anoptical/electric signal) may be selectively formed, thus, enablingwavelength analysis and the use as an optical sensor, an electricswitch, etc. Therefore, metal chalcogenide thin films havingcompositional deviations would have beneficial applications.

SUMMARY

An aspect of the some example embodiments provides metal chalcogenidethin films having a compositional variation.

Another aspect of the some example embodiments provides a method ofmanufacturing the metal chalcogenide thin films.

Another aspect of the some example embodiments provides a device formanufacturing the metal chalcogenide thin films.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the example embodiments.

According to an aspect of some example embodiments, provided is a metalchalcogenide thin film including a transition metal element and achalcogen element, wherein at least one of the transition metal elementand the chalcogen element has a composition gradient along a surface ofthe metal chalcogenide thin film, the composition gradient being anin-plane composition gradient.

According to another aspect of some example embodiments, provided is amethod of preparing a metal chalcogenide thin film, the methodincluding: providing a transition metal precursor and a chalcogenprecursor on a substrate by using a confined reaction space, wherein atleast one of the transition metal precursor and the chalcogen precursorforms a concentration gradient according to a position on a surface of asubstrate; and heat treating the confined reaction space.

According to another aspect of some example embodiments, provided is adevice for manufacturing the metal chalcogenide thin film describedabove, the device including: a confined reaction space configured tohold a substrate inside the confined reaction space or have thesubstrate form a side of the confined reaction space, the confinedreaction space including at least one inlet configured to provide atleast one of a transition metal precursor and a chalcogen precursor toform a concentration gradient according to a position on the surface ofthe substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1A shows a schematic view of a device for manufacturing a metalchalcogenide thin film according to some example embodiments;

FIG. 1B shows a graph of the concentration of a precursor with respectto a position on the substrate in the manufacturing device;

FIG. 1C shows an image of a metal chalcogenide thin film manufactured byusing the manufacturing device;

FIG. 1D is a graph showing results obtained by measuring binding energyat a Mo-rich region of the metal chalcogenide thin film;

FIG. 1E is a graph showing results obtained by measuring binding energyat a Mo-deficient region of the metal chalcogenide thin film;

FIG. 1F shows positions for the measurement of the thickness differenceand the optical bandgap according to a region of the metal chalcogenidethin film;

FIG. 1G shows a graph of a result of the measurement of the opticalbandgap of the metal chalcogenide thin film according to the position onthe metal chalcogenide thin film;

FIG. 2A shows a schematic view of a device for manufacturing a metalchalcogenide thin film according to some example embodiments;

FIG. 2B shows an image of a metal chalcogenide thin film manufactured byusing the manufacturing device, wherein the composition and thickness ofa transition metal element continuously change;

FIG. 3A shows a schematic view of a device for manufacturing a metalchalcogenide thin film according to some example embodiments;

FIG. 3B shows an image of a metal chalcogenide thin film manufactured byusing the manufacturing device, wherein the composition and thickness ofa chalcogen element continuously change;

FIG. 4 shows a schematic view of a device for manufacturing a metalchalcogenide thin film according to some example embodiments; and

FIG. 5 shows examples in which a metal chalcogenide thin film accordingto some example embodiments is used as an element.

FIG. 6 shows examples in which a metal chalcogenide thin film accordingto some example embodiments is used as an element.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theexample embodiments are merely described below, by referring to thefigures, to explain aspects. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list.

The present inventive concepts will now be described more fully withreference to the accompanying drawings, in which example embodiments areshown. The present inventive concepts may, however, be embodied in manydifferent forms, should not be construed as being limited to the exampleembodiments set forth herein, and should be construed as including allmodifications, equivalents, and alternatives within the scope of thepresent inventive concept; rather, these embodiments are provided sothat this inventive concepts will be thorough and complete, and willfully convey the effects and features of the present inventive conceptsand ways to implement the present inventive concepts to those skilled inthe art.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

In the drawings, the size or thickness of each layer, region, or elementare arbitrarily exaggerated or reduced for better understanding or easeof description, and thus the present inventive concepts is not limitedthereto. Throughout the written description and drawings, like referencenumbers and labels will be used to denote like or similar elements. Itwill also be understood that when an element such as a layer, a film, aregion or a component is referred to as being “on” another layer orelement, it can be “directly on” the other layer or element, orintervening layers, regions, or components may also be present. Althoughthe terms “first”, “second”, etc., may be used herein to describevarious elements, components, regions, and/or layers, these elements,components, regions, and/or layers should not be limited by these terms.These terms are used only to distinguish one component from another, notfor purposes of limitation.

It will be understood that, although the terms first, second, third,etc., may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms.

In regard to manufacturing processes described herein, the manufacturingprocesses may not be carried out in the stated order. For example, incases where a first step and a second step are described, it will beunderstood that the first step does not necessarily precede the secondstep.

Hereinafter, a metal chalcogenide thin film according to exampleembodiments, and a method and device for manufacturing the same will bedescribed in more detail.

A metal chalcogenide thin film according to some example embodimentsincludes a transition metal element and a chalcogen element, and atleast one of the transition metal element and the chalcogen element hasa composition gradient along the surface of the metal chalcogenide thinfilm, that is, an in-plane composition gradient.

A metal chalcogenide compound exhibits different bandgaps depending onthe composition ratio of transition metal alloy or chalcogen alloy.Unlike conventional metal chalcogenide thin films studied so far, whichhave a constant in-plane composition, in the case of the metalchalcogenide thin film according to some example embodiments, a locationwhere a precursor of a transition metal element and/or a chalcogenelement is provided is controlled by using a confined reaction space,thereby inducing a compositional variation according to a position of athin film, that is, an in-plane composition gradient.

In the case of the metal chalcogenide thin film, a desired bandgapcharacteristic is obtained by forming an in-plane composition gradientin a single thin film by using an alloy of various transition metals andchalcogen elements. Thus, the metal chalcogenide thin film is applicableto various electronic elements, such as a light wavelength sensor.

In relation to the in-plane composition gradient of the metalchalcogenide thin film, a composition may continuously change from anelement-rich region to an element-deficient region in a thin film.

According to some example embodiments, the metal chalcogenide thin filmmay include a composition represented by the following Formula 1.M_(1-x)M′_(x)X_(2(1-y))X′_(2y)  [Formula 1]

wherein M and M′ are different transition metal elements, X and X′ aredifferent chalcogen elements, 0≤x<1, and 0≤y<1, and at least one of xand y is not 0.

The transition metal element may be selected from, for example, Ti, Zr,Hf, V, Nb, Ta, Mo, W, Tc, Re, Co, Rh, Ir, Ni, Pd, Pt, Zn, and/or Sn, andmay be, for example, Mo, W, V, Nb, and/or the like.

The chalcogen element may be selected from, for example, S, Se, and/orTe.

In this regard, at least one of the transition metal element and thechalcogen element shows a composition gradient along the surface of thethin film. In other words, x or y, or x and y, may be continuouslychanged along the surface of the metal chalcogenide thin film.

The metal chalcogenide thin film may include, for example, a compositionrepresented by Formula 2.Mo_(1-x)W_(x)S_(2(1-y))Se_(2y)  [Formula 2]

wherein 0≤x<1 and 0≤y<1, and at least one of x and y is not 0.

According to some example embodiments, the transition metal element andthe chalcogen element may each exhibit an in-plane composition gradient.At this time, the composition gradient of the transition metal elementand the composition gradient of the chalcogen element may beperpendicular to each other along the surface of the metal chalcogenidethin film.

According to some example embodiments, the metal chalcogenide thin filmmay have a thickness variation as well as the compositional variation ina plane thereof. For example, in regard to the composition gradient ofthe metal chalcogenide thin film, the thickness of the element-richregion may be greater than that of the element-deficient region, and thethickness of the metal chalcogenide thin film may decrease substantiallycontinuously from the element-rich region to the element-deficientregion. As described above, by having not only the compositionalvariation but also the thickness variation, the bandgap changecharacteristic according to the position of a thin film may be bettercontrolled.

The metal chalcogenide thin film can be applied to an electronic elementsuch as an optical wavelength sensor having a desired bandgap region.Due to such a characteristic of the metal chalcogenide thin film thatthe electric and optical bandgap changes according to a compositionaldeviation, a region that is turned on depending on the input energy bandof an optical/electric signal is selectively generated, enablingwavelength analysis and the use as an optical sensor, an electricswitch, etc.

For example, as shown in FIG. 5 , when a metal chalcogenide thin filmhaving the composition MoS_(2(1-y)) Se_(y) is taken as an example, whentransition metal regions having different bandgaps according to thecomposition variation are patterned and separated, and then, anelectrode is attached on each of the transition metal regions, a regionthat undergoes channeling according to a characteristic of radiatedlight is generated, enabling wavelength analysis and the use as anoptical sensor. In this regard, when the composition of the transitionmetal or chalcogen is increased, the bandgap energy band may be furtherexpanded. For example, when MoS₂ is used alone, the bandgap may be fromabout 1.3 eV to about 1.8 eV, and once an element is introduced, thebandgap may be widened from about 0.8 eV to about 3.5 eV.

When the terms “about” or “substantially” are used in this specificationin connection with a numerical value, it is intended that the associatednumerical value include a tolerance of ±10% around the stated numericalvalue. When ranges are specified, the range includes all valuestherebetween such as increments of 0.1%.

For example, as shown in FIG. 6 , when a metal chalcogenide thin filmhaving the composition having a composition gradient in two directionsis taken as an example, when transition metal regions having differentbandgaps according to the composition variation are patterned andseparated, and then, an electrode is attached on each of the transitionmetal regions, a region that undergoes channeling according to acharacteristic of radiated light is generated, enabling wavelengthanalysis and the use as an optical sensor. In this regard, when thecomposition of the transition metal or chalcogen is increased, thebandgap energy band may be further expanded. For example, when MoS₂ isused alone, the bandgap may be from about 1.3 eV to about 1.8 eV, andonce an element is introduced, the bandgap may be widened from about 0.8eV to about 3.5 eV.

Such a metal chalcogenide thin film may be produced by using thefollowing method using a confined reaction space.

A method of manufacturing the metal chalcogenide thin film according tosome example embodiments includes:

providing a transition metal precursor and a chalcogen precursor on asubstrate by using a confined reaction space, wherein at least one ofthe transition metal precursor and the chalcogen precursor forms aconcentration gradient according to a position on the surface of thesubstrate; and

heat treating the confined reaction space.

Herein, the wording “confined reaction space” refers to a space that issmaller than a general reaction chamber, and a space in which a metalchalcogenide compound is formed on a substrate by reacting a transitionmetal precursor and a chalcogen precursor, is limited by, for example, acontainer. To make a desired concentration variation of a precursorwithin the space, the size and shape of the space, the location of aninlet, the location of an outlet, and the loading and discharging speedof a precursor, etc. are controlled to make a target design change.

By using the confined reaction space, at least one of the transitionmetal precursor and the chalcogen precursor may be provided to form aconcentration gradient depending on a position on the surface of thesubstrate. To this end, at least one of the transition metal precursorand the chalcogen precursors may be provided in a vapor phase in ahorizontal direction on the surface of the substrate. By doing so,during the deposition of the metal chalcogenide compound, thecomposition gradient of a precursor is formed along the position on thesurface of the substrate, and thus, the precursor may be grown into ametal chalcogenide thin film having an in-plane composition gradient ina single thin film.

The substrate may be placed inside or on one side of the confinedreaction space.

The substrate is a supporting substrate for growing a metal chalcogenidethin film, and may include at least one selected from silicon, siliconoxide, aluminum oxide, magnesium oxide, silicon carbide, siliconnitride, glass, quartz, sapphire, graphite, graphene, polyimidecopolymer, polyimide, polyethylene naphthalate (PEN), fluoropolymer(FEP), and/or polyethylene terephthalate (PET).

The substrate may include, for example, a silicon (Si) substrate. Atthis time, silicon oxide may further be positioned on the Si substrate.

The substrate may be placed inside a confined reaction space, or an openside of a reaction vessel may be covered by a substrate to form aconfined reaction space

The confined reaction space with the substrate provided may beheat-treated at a temperature which is suitable for the growth of a thinfilm by using a separate heater.

The confined reaction space may be provided with an inlet through whicha transition metal precursor and/or a chalcogen precursor is provided,and at least one of the transition metal precursor and the chalcogenprecursor may be provided to form a concentration gradient depending onthe position on the surface of the substrate.

The transition metal precursor may include at least one element selectedfrom Ti, Zr, Hf, V, Nb, Ta, Mo, W, Tc, Re, Co, Rh, Ir, Ni, Pd, Pt, Zn,and/or Sn. For example, the transition metal precursor may include ametal oxide, a metal halide, a metal carbonyl compound, and/or acombination thereof, each including the element.

An example of the metal oxide may include at least one selected fromMoO₃, MoO, MoO₂, WO₂, WO₃, VO, VO₂, V₂O₃, V₂O₅, V₃O₅, NbO, NbO₂, Nb₂O₅,TaO, TaO₂, Ta₂O₅, TiO, TiO₂, Ti₂O₃, Ti₃O₅, ZrO₂, HfO₂, TcO₂, Tc₂O₇,ReO₂, ReO₃, Re₂O₃, Re₂O₇, CoO, CO₂O₃, Co₃O₄, Rh₂O₃, RhO₂, IrO₂, Ir₂O₃,IrO₂.2H₂O, NiO, Ni₂O₃, PdO, PdO₂, PtO, PtO₂, PtO₃, Pt₃O₄, PtO₂—H₂O, GaO,Ga₂O, Ga₂O₃, SnO, and/or SnO₂.

An example of the metal halide may include at least one selected fromMoF₃, MoF₆, MoF₄, Mo₄F₂O, MoCl₂, MoCl₃, MoCl₆, MoCl₄, MoCl₅, MoBr₃,MoBr₄, MoI₂, MoI₃, MoI₄, WF₆, WF₄, [WF₅]₄, WCl₂, WCl₆, WCl₄, [WC₅]₂,[W₆Cl₁₂]Cl₆, WBr₃, WBr₆, WBr₄, WBr₅, W₆Br₁₄, WI₂, WI₃, WI₄, VF₂, VF₃,VF₄, VF₅, VCl₂, VCl₃, VCl₄, VBr₂, VBr₃, VBr₄, Vl₂, Vl₃, Vl₄, NbCl₃,NbCl₄, NbCl₅, NbBr₄, NbBr₅, NbI₃, NbI₄, Nb₅, TaF₃, [TaF₅]₄, TaCl₃,TaCl₄, TaCl₅, TaBr₃, TaBr₄, TaBr₅, Ta₄, Ta₅, TiF₂, TiF₃, TiF₄, TiCl₄,TiCl₃, TiCl₂, TiBr₃, TiBr₄, HfCl₄, HfBr₂, HfBr₄, HfI₃, HfI₄, ZrF₄,ZrCl₂, ZrCl₃, ZrCl₄, ZrBr₃, ZrBr₄, ZrI₂, ZrI₃, ZrI₄, TcF₆, TcF₅, TcCl₄,TcCl₆, TcBr₄, ReF₆, ReF₄, ReF₅, ReF₇, Re₃Cl₉, ReCl₅, ReCl₄, ReCl₆,ReBr₃, ReBr₄, ReBr₅, ReI₃, ReI₄, CoF₂, CoF₃, CoF₄, CoCl₂, CoCl₃, CoBr₂,CoI₂, RhF₃, RhF₆, RhF₄, [RhF₅]₄, RhCl₃, RhBr₃, RhI₃, IrF₃, IrF₆, IrF₄,[IrF₅]₄, IrCl₂, IrCl₃, IrCl₄, IrBr₂, IrBr₃, IrBr₄, IrI₂, IrI₃, IrI₄,NiF₂, NiCl₂, NiBr₂, NiI₂, PdF₂, PdF₄, PdCl₂, PdBr₂, PdI₂, PtF₆, PtF₄,[PtF₅]₄, PtCl₂, PtCl₃, PtCl₄, Pt₆Cl₁₂, PtBr₂, PtBr₃, PtBr₄, PtI₂, PtI₃,PtI₄, GaF₃, GaCl₂, GaCl₃, GaBr₃, GaI₃, SnF₂, SnF₄, SnCl₂, SnCl₄, SnBr₂,SnBr₄, SnI₂, and/or SnI₄.

An example of the metal carbonyl compound may include at least oneselected from Mo(CO)₆, W(CO)₆, Nb(CO)₆, V(CO)₆, Ta(CO)₆, Ti(CO)₆,Zr(CO)₇, Tc₂(CO)₁₀, Hf(CO)₇ Re₂(CO)₁₀, CO₂(CO)₈, CO₄(CO)₁₂, CO₆(CO)₁₆,Rh₂(CO)₈, Rh₄(CO)₁₂, Rh₆(CO)₁₆, Ir₂(CO)₈, Ir₄(CO)₁₂, Ir₆(CO)₁₆, Ni(CO)₄,Pd(CO)₄, and/or Pt(CO)₄.

For the transition metal precursor, a precursor in a vapor state may beused, or a precursor in a powder state such as molybdenum oxide (MoO₃)may be vaporized and then provided on a substrate.

The chalcogen precursor may include at least one element selected fromS, Se, and/or Te.

The chalcogen precursor may include at least one selected from, forexample, sulfur, hydrogen sulfide (H₂S), diethyl sulfide, dimethyldisulfide, ethyl methyl sulfide, (Et₃Si)₂S, selenium vapor, hydrogenselenide (H₂Se), diethyl selenide, dimethyl diselenide, ethyl methylselenide, (Et₃Si)₂Se, telenium vapor, hydrogen telluride (H₂Te),dimethyl telluride, diethyl telluride, ethyl methyl telluride, and/or(Et₃Si)₂Te.

The chalcogen precursor may include, for example, a chalcogen-containinggas, such as S₂, H₂S, Se₂, Te₂, H₂Se, H₂Te, and/or the like.

FIG. 1A shows a schematic view of an example of a device formanufacturing a metal chalcogenide thin film according to some exampleembodiments.

As illustrated in FIG. 1A, for example, when a transition metalprecursor in a powder state, such as MoO₃, is used to form aconcentration gradient according to a position on the surface of asubstrate, the substrate is arranged to form one side of a confinedreaction space, and the transition metal precursor in a powder state isplaced on an inner bottom of the confined reaction space to face thesubstrate. To this end, a transition metal precursor in a powder state,such as MoO₃, is placed inside an open reaction vessel, which is thencovered with a substrate to form a confined reaction space.

In this case, when the transition metal precursor in a powder state isvaporized by heating, due to the location of the transition metalprecursor placed close to the center of the substrate, the transitionmetal precursor has a high concentration at the center of the substrateand has a smaller concentration away from the center of the substrate bydiffusion.

When the transition metal precursor in a powder state is vaporized anddiffused by heating, as illustrated in FIG. 1B, in regard to the surfaceof the substrate, a region that is closer to the location of thetransition metal precursor may be controlled to have a highconcentration of the precursor, and a region that is farther from thelocation of the transition metal precursor may be controlled to have alow concentration of the precursor.

At this time, the chalcogen precursor may be injected in a vapor statesuch as sulfur gas into the confined reaction space while theconcentration thereof is maintained constant. In other exampleembodiments, the chalcogen precursor may be provided to form aconcentration gradient.

For example, as illustrated in FIG. 1A, when the chalcogen precursor,such as sulfur (S) gas, is injected at a high concentration through aninlet formed between the confined reaction space and the substrate anddischarged at a high speed through an outlet located opposite to theinlet of the confined reaction space, as illustrated in FIG. 1B, of thesurface of the substrate, a region that is closer to the inlet has ahigher concentration of the S precursor, and a region that is closer tothe outlet has a lower concentration of the S precursor, that is, aconcentration gradient may be formed.

When the transition metal precursor and the chalcogen precursor areprovided in the concentration conditions described with reference toFIG. 1B by using the manufacturing device of FIG. 1A, a metalchalcogenide thin film having the in-plane composition gradient shown inFIG. 1C may be formed. This is a metal chalcogenide thin film preparedaccording to Example 1, to be described later.

As shown in FIG. 1C, a metal chalcogenide thin film may be formed inwhich a region having a high concentration of the transition metalprecursor is rich with Mo (indicated by Mo-rich) and a region having alow concentration of the transition metal precursor is deficient with Mo(indicated by Mo-deficient). When a precursor is provided with theconcentration gradient as illustrated in FIG. 1B, a metal chalcogenidethin film may be formed in which a Mo-rich region is formed at thecenter thereof and a Mo-deficient region is formed away from the centerthereof, a left portion is S-rich, and a right portion is S-deficient.

When the metal chalcogenide thin film of FIG. 1C has a thicknessvariation as well as the composition gradient, in the Mo-rich region atthe center of the metal chalcogenide thin film, more MoS₂ may bedeposited, and away from the center of the metal chalcogenide thin film,less MoS₂ may be deposited.

The results obtained by measuring the binding energy of the Mo-richregion and the Mo-deficient region of the metal chalcogenide thin filmare shown in FIG. 1D and FIG. 1E, respectively.

By changing the position of the transition metal precursor in a powderstate, the position of the maximum concentration of the correspondingtransition metal element may be changed. For example, the transitionmetal precursor in a powder state may be arranged to be verticallyspaced from the surface of the substrate.

According to some example embodiments, the transition metal precursormay have a concentration gradient with the greatest concentration in themiddle of the surface of the substrate, or the greatest concentrationmay be at another point on the surface of the substrate. Additionally,the chalcogenide may have a concentration gradient with the greatestconcentration at any point along the surface of the substrate. In someexample embodiments there may be two or more areas with the greatestconcentration of a transition metal precursor and/or a chalcogenide.

In another example embodiment, the transition metal precursor and/or thechalcogenide may have a concentration gradient along two axis of thesubstrate, such that a concentration gradient changes along a firstdirection and a concentration gradient change along a second direction.For example, a point on the surface of the substrate may have a greatestconcentration, and the concentration may go down in a first directionaccording to a first concentration gradient, and may go down in a seconddirection according to a second concentration gradient.

According to some example embodiments, two or more different kinds oftransition metal precursors or chalcogen precursors may be introduced ina vapor state into the confined reaction space in different directionsto form a concentration gradient according to a position on the surfaceof the substrate.

FIG. 2A shows a schematic view of an example of a device formanufacturing a metal chalcogenide thin film according to some exampleembodiments.

As shown in FIG. 2A, the substrate is placed to form one side of aconfined reaction space. For example, an upper portion of an openreaction vessel may be covered with the substrate. Through inlets (A andB) at opposite sides of the confined reaction space, two different kindsof transition metal precursors (M source and M′ source) are injected ina vapor state in opposite directions to form a concentration gradientaccording to the position on the surface of the substrate.

In some example embodiments, a transition metal precursor (X source) maybe injected in a vapor state in such a manner that the concentrationthereof is maintained constant regardless of a position on the surfaceof the substrate. In this case, the inlet C for the transition metalprecursor may be formed in a lower surface of the confined reactionspace, but the location of the inlet C is not limited thereto.

When a transition metal precursor and a chalcogen precursor are providedby using the manufacturing device of FIG. 2A, as shown in FIG. 2B, ametal chalcogenide thin film having the composition M_(1-x)M′_(x)X₂(where 0<x<1) may be formed to have an in-plane composition gradient inwhich a left portion is M-rich and a right portion is M′-rich. Here, themetal chalcogenide thin film may have a thickness variation in which theM-rich region and the M′-rich region are each thick and the centralportion is thin.

FIG. 3A shows a schematic view of an example of a device formanufacturing a metal chalcogenide thin film according to some exampleembodiments.

As shown in FIG. 3A, the substrate is placed on one side of a confinedreaction space. Through inlets (C and D) at opposite sides of theconfined reaction space, two different kinds of chalcogen precursors (Xsource and X′ source) are injected in a vapor state in oppositedirections to form a concentration gradient according to a position onthe surface of the substrate. In some example embodiments, a chalcogenprecursor (M source) may be injected in a vapor state in such a mannerthat the concentration thereof is maintained constant regardless of aposition on the surface of the substrate. In this case, the inlet A forthe chalcogen precursor may be formed in a lower surface of the confinedreaction space, but the location of the inlet A is not limited thereto.

When a transition metal precursor and a chalcogen precursor are providedby using the manufacturing device of FIG. 3A, as shown in FIG. 3B, ametal chalcogenide thin film having the composition MX_(2(1-y))X′_(2y)(where 0<y<1) may be formed to have an in-plane composition gradient inwhich a left portion is X-rich and a right portion is X′-rich. Here, themetal chalcogenide thin film may have a thickness variation in which theX-rich region and the X′-rich region are each thick and the centralportion is thin.

According to some example embodiments, a substrate is placed on one sideof a confined reaction space, two different kinds of transition metalprecursors are injected in a vapor state in opposite directions of theconfined reaction space to form a concentration gradient according to aposition on the surface of a substrate, and also, two different kinds ofchalcogen precursors are injected in a vapor state in oppositedirections of the confined reaction space to form a concentrationgradient according to a position on the surface of the substrate. Here,the directions in which the transition metal precursors and thechalcogen precursors are injected may be perpendicular to each other.

As such, formed are four or more components of a metal chalcogenide thinfilm in which the transition metal and the chalcogen element each have acomposition gradient. The metal chalcogenide thin film may have thecomposition represented by M_(1-x)M′_(x) X_(2(1-y))X′_(2y) (where 0<x<1and 0<y<1).

In regard to the method of manufacturing the metal chalcogenide thinfilm, in the confined reaction space to which the transition metalprecursor and the chalcogen precursor are provided, a 2-dimensionalmetal chalcogenide thin film may be grown by a heat treatment.

According to some example embodiments, the heat treatment may beperformed at a temperature higher than the volatilization temperature ofa transition metal precursor used in the manufacture of a thin film. Forexample, in the case of MoS₂, when the heat treatment temperature is 750□ or higher, the volatilization of a MoO₃ precursor may be induced, andin a vaporized sulfur gas atmosphere, a metal chalcogenide thin film isgrown in a two-dimensional plane. At the heat treatment temperaturelower than 750 □, when the MoO₃ precursor is exposed to vaporized sulfurgas, the MoO₃ precursor may not be volatilized and may itself be reducedinto a metal oxide, such as MoO₂, or after the metal oxide is formed onthe substrate, the metal oxide is sulfided and instead of the growth ofa thin film on the substrate, a vertically grown metal chalcogenide maybe formed. In the case of MoS₂, the heat treatment may be performed in arange of about 750 □ to about 1100 □, or 750 □ to 1100 □.

A device for manufacturing a metal chalcogenide thin film according tosome example embodiments includes a confined reaction space, and asubstrate placed inside the confined reaction space or on one side ofthe confined reaction space, wherein the confined reaction space has atleast one inlet through which at least one of a transition metalprecursor and a chalcogen precursor is provided to form a concentrationgradient according to a position on the surface of a substrate.

By using the manufacturing device, a metal chalcogenide thin film may beformed in which at least one of a transition metal element and achalcogen element shows a composition gradient along the surface of themetal chalcogenide thin film, that is, an in-plane composition gradient.

According to some example embodiments, the inlet may be formed in a sidesurface of the confined reaction space in such a manner that at leastone of the transition metal precursor and the chalcogen precursor isprovided in a vapor state in a direction parallel to the surface of thesubstrate.

According to some example embodiments, the confined reaction space mayfurther include an outlet for controlling the concentration of one ofthe transition metal precursor and the chalcogen precursor.

Examples of the device for manufacturing the metal chalcogenide thinfilm according to various example embodiments are schematicallyillustrated in FIGS. 1A, 2A, 3A, and 4 , but are not limited thereto.

Example embodiments are explained in detail through Examples andComparative Examples. It should be noted, however, that the exampleembodiments are for illustrative purposes only and are not intended tolimit the scope of the present disclosure.

Example 1

By using the manufacturing device schematically illustrated in FIG. 1A,a transition metal precursor and a chalcogen precursor are providedaccording to a concentration condition for a substrate as illustrated inFIG. 1B to form a metal chalcogenide thin film having an in-planecomposition gradient and the composition MoS₂.

In detail, 30 mg of MoO₃ powder and 80 mg of S powder were used tomanufacture a MoS₂ thin film. A substrate was located on top of acrucible containing MoO₃ powder to allow volatilized MoO_(x) gas tomaintain a high partial pressure in a space confined by the crucible andthe substrate, and before the crucible, Ar gas was used as a carryinggas to smoothly provide the volatilized sulfur gas, and sulfur providedby the carrying gas was reacted with a high concentration of MoO_(x)gas, thereby completing the manufacture of a metal chalcogenide thinfilm having an in-plane Mo concentration gradient and sulfurconcentration gradient. For a smooth production, the process was carriedout at a temperature of 780° C. for 10 minutes, and the process pressurewas 1 Torr.

An image of the metal chalcogenide thin film prepared according toExample 1 is shown in FIG. 1C. As shown in FIG. 1C, a metal chalcogenidethin film may be formed in which a Mo-rich region is located at thecenter (where MoO₃ is located) thereof, and away from the center of thethin film, Mo is deficient, and an S-deficient composition gradient maybe formed from close to the inlet of sulfur to away from the inlet ofthe sulfur.

FIG. 1D is a graph showing the results obtained by measuring the bindingenergy of the Mo-rich region of the metal chalcogenide thin film, andFIG. 1E is a graph showing the results obtained by measuring the bindingenergy of the Mo-deficient region of the metal chalcogenide thin film.

As can be seen from FIG. 1D and FIG. 1E, the total amount of Mo⁶⁺Mo6+and Mo⁵⁺ observed in the Mo-rich region is greater than that in theMo-deficient region, indicating that Mo in the Mo-rich region is richerthan in the Mo-deficient region.

To identify an optical bandgap according to a position on the metalchalcogenide thin film, luminescence spectra were measured by using aWITEC Alpha 300R at the positions P1 to P7 shown in FIG. 1F, and theresults are shown in FIG. 1G.

As shown in FIG. 1G, it can be seen that the optical bandgap OBG of thethin film changes from 1.82 eV to 1.85 eV depending on the position, andfrom the results, it was confirmed that the optical bandgap changesdepending on the concentrations of Mo and S.

A metal chalcogenide thin film according to some example embodiments hasa composition gradient along the surface thereof, that is, an in-planecomposition gradient, thereby achieving various desired bandgapcharacteristics. The metal chalcogenide thin film may be easily preparedby using a confined reaction space.

It should be understood that example embodiments described herein shouldbe considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exampleembodiment should typically be considered as available for other similarfeatures or aspects in other example embodiments. While one or moreexample embodiments have been described with reference to the figures,it will be understood by those of ordinary skill in the art that variouschanges in form and details may be made therein without departing fromthe spirit and scope as defined by the following claims.

What is claimed is:
 1. A metal chalcogenide thin film comprising: atransition metal element; and a chalcogen element, wherein at least oneof the transition metal element and the chalcogen element has acomposition gradient along a surface of the metal chalcogenide thinfilm, the composition gradient being an in-plane composition gradient, athickness of the metal chalcogenide thin film continuously decreaseswith the composition gradient.
 2. The metal chalcogenide thin film ofclaim 1, wherein the metal chalcogenide thin film includes a compositionrepresented by Formula 1:M_(1-x)M′_(x)X_(2(1-y))X′_(2y)  [Formula 1] wherein M and M′ aredifferent transition metal elements, X and X′ are different chalcogenelements, 0≤x<1, and 0≤y<1, and at least one of x and y is not
 0. 3. Themetal chalcogenide thin film of claim 2, wherein the transition metalelement is selected from Ti, Zr, Hf, V, Nb, Ta, Mo, W, Tc, Re, Co, Rh,Ir, Ni, Pd, Pt, Zn, and Sn, and the chalcogen element is selected fromS, Se, and Te.
 4. The metal chalcogenide thin film of claim 1, whereineach of the transition metal element and the chalcogen element shows anin-plane composition gradient.
 5. The metal chalcogenide thin film ofclaim 4, wherein a composition gradient of the transition metal elementand a composition gradient of the chalcogen element are perpendicular toeach other along a surface of the metal chalcogenide thin film.